1. Field of the Invention
The present invention relates to a multistage lock, especially to a multistage lock that opens an outer frame and an inner frame of a door (window) in series.
2. Description of the Prior Art(s)
Openings that are reserved on walls of a building allow people, light and wind to pass through. A door panel (window) is mounted on the building in the opening to selectively open or close the opening of the building. However, when a conventional door panel (window) is opened, the opening of the building is also totally opened. If indoor people are unaware of the outdoor situation before opening the conventional door (window), danger may happen; or when the conventional door (window) is unable to partly open due to outdoor weathers, a clean indoor environment may be ruffled by the wind.
In view of the abovementioned shortcomings, a conventional main door panel (window) having a conventional additional door panel (window) is designed to allow people to open the additional door panel (window) to determine the outdoor situation or to ventilate indoor air. However, since the conventional main door panel (window) and the conventional additional door panel (window) are driven respectively by two handle assemblies, lock mechanism for the conventional door panels (windows) is complicated.
To overcome the shortcomings, the present invention provides a multistage lock to mitigate or obviate the aforementioned problems.